docs: def chromaticity_to_XYZ(white, red, green, blue):
      """From the "CalRGB Color Spaces" section of "PDF Reference", 6th ed."""
      xW, yW = white
      xR, yR = red
      xG, yG = green
      xB, yB = blue
      R = G = B = 1.0
  
      z = yW * ((xG - xB) * yR - (xR - xB) * yG + (xR - xG) * yB)
      YA = yR / R  * ((xG - xB) * yW - (xW - xB) * yG + (xW - xG) * yB) / z
      XA = YA * xR / yR
      ZA = YA * ((1 - xR) / yR - 1)
      YB = - yG / G * ((xR - xB) * yW - (xW - xB) * yR + (xW - xR) * yB) / z
      XB = YB * xG / yG
      ZB = YB * ((1 - xG) / yG - 1)
      YC = yB / B * ((xR - xG) * yW - (xW - xG) * yR + (xW - xR) * yG) / z
      XC = YC * xB / yB
      ZC = YC * ((1 - xB) / yB - 1)
      XW = XA * R + XB * G + XC * B
      YW = YA * R + YB * G + YC * B
      ZW = ZA * R + ZB * G + ZC * B
  
      return (XW, YW, ZW), (XA, YA, ZA), (XB, YB, ZB), (XC, YC, ZC)